1. Field of the Invention
The present invention relates to a projection display apparatus for displaying an image on a projection plane, and more particularly, is suited for use in a projection display apparatus that is mounted on the projection plane.
2. Description of the Related Art
Conventionally, in projection display apparatuses (projectors), types of the projectors that project an image onto a screen, wall surface or the like have been common. Recently, in keeping up with a trend towards compact configurations, there have been proposed projectors that are mounted on a desk and project an image onto a desktop surface (hereinafter, referred to as “desk mountable projector”). In such a desk mountable projector, however, since a distance between a position from which projection light is emitted and a projection plane (desktop surface) is significantly short, it is difficult to shift a group of zoom adjustment lenses of the projector to perform focus adjustment in terms of an optical design. On the other hand, a zoom function has been a major advantage of the conventional projectors, and thus needs to be also incorporated into the desk mountable projectors.
Besides zoom adjustment, focus adjustment is an essential function of the projectors. Generally, focus adjustment is made in accordance with a change in a zoom state. More specifically, focus adjustment is carried out as appropriate to eliminate a blur in a projection image caused by the change in the zoom state. Therefore, important issues in the desk mountable projectors are to use a proper zoom adjustment method and to achieve a focus adjustment function in cooperation with the zoom adjustment method.